1. Field of the Invention
The present invention relates to a coupling fan which is employed in an automobile engine cooling system or the like.
2. Description of the Related Art
A fan is disposed in an automobile engine cooling system, and it is driven by rotations of an engine which is adapted for the driving source. The fan rotates to deliver winds to a radiator, thereby carrying out the heat exchange between hot cooling water and cold cooling water in the radiator. So far, this fan has been connected mechanically to an engine crank shaft by means of a belt or the like, and it has been directly driven rotatively. However, a coupling fan which is indirectly driven rotatively by means of fluid viscous resistance has come to be employed recently.
As illustrated in FIG. 13, this coupling fan includes a fan body 100 and a mounting plate 200. The fan body 100 is installed to a coupling 300 by way of the mounting plate 200.
The fan body 100 includes a cylinder-shaped boss 101, and a plurality of blades 102 which are disposed on an outer peripheral surface of the boss 101 at predetermined intervals in a circumferential direction and which project substantially radially. When the fan body 100 rotates, the blades 102 deliver winds from a radiator which is disposed at a position opposite to the coupling 300.
The mounting plate 200 is a thin plate-shaped member, and it is formed in a ring-like shape which has an opening at a center thereof. This mounting plate 200 is fixed to the boss 101 of the fan body 100, and at the same time it is fixed to an operating member 301 of the coupling 300.
The coupling 300 mainly includes a driving shaft 302 which is connected to an engine crank shaft, a driving plate 303 which is connected to the driving shaft 302, an operating member 301 which is disposed at a position opposite to the driving plate 303 and rotatably held by the driving shaft 302, and a silicone oil which is interposed between the operating member 301 and the driving plate 303. Rotary forces of the driving plate 303 are transmitted to the operating member 301 by way of viscous resistance of the silicone oil, and they rotate the fan body 100 by way of the mounting plate 200 which is installed to the operating member 301.
As high output performance has been required for automobile engines recently, vibrations of coupling fans which are connected to the automobile engines have enlarged. Accordingly, improvement has been longed for durability of the coupling fans. In Unexamined Japanese Utility Model Publication (Kokai) No. 660,994/1981, a vibration isolator type coupling fan is disclosed. In the coupling fan, a mounting plate is provided with a spring operation in order to give a vibration damping performance to the coupling fan. As illustrated in FIG. 14, this mounting plate includes a ring-shaped base member 400 and a plurality of extending members 401 which project radially inward from the base member 400 and which extend in a circumferential direction. The base member 400 is provided with a plurality of holes 402, whereby it is fixed to a fan body 100. In addition, a guide surface 403 is disposed at a front end of the extending members 401. The guide surfaces 403 are brought into contact with a coupling 300, thereby positioning the mounting plate. A hole 404 is further disposed at the front end of the extending members 401, whereby the extending members 401 are fixed to an operating member 301 of the coupling 300. All in all, the entire mounting plate is formed of a plate spring, and accordingly it is intended to absorb vibrations mainly in an axial direction by means of spring elasticity of the extending members 401.
In the above-described coupling fans, it has been known that durability of the viscous substance such as the silicone oil filled therein affects engine cooling performance of the coupling fan greatly. In short, as the viscous substance degrades, its viscosity degrades. Hence, the rotary forces of the driving plate 303 cannot be transmitted to the operating member 301 sufficiently, thereby resulting in reduction of a number of revolutions of the fan body 100. Most of the degradation of the filled viscous substance results from heat. Therefore, it is preferred to cool the coupling 300 and thereby cool the viscous substance in order to inhibit the viscous substance from degrading. Accordingly, it is possible to think of improving the cooling efficiency by increasing an outside diameter of the coupling 300 so as to enlarge an area of cooling fins 304 which are formed on a surface of the coupling 300 illustrated in FIG. 13.
However, it has been very crowded in automobile engine rooms recently. Hence, it is not preferred to enlarge a size of the fan body 100. Consequently, it is preferred to enlarge an outside diameter of the coupling 300 only while maintaining a current configuration of the fan body 100. If such is possible, however, the mounting plate 200 should be down-sized in width. Even when a coupling fan employs the mounting plate illustrated in FIG. 14 which has the vibration damping performance, the extending members 401 should be down-sized in width as well, and such down-sizing results in a strength problem. In the worst case, the mounting plate cannot be provided with the extending members 401.
In addition, in the mounting plate illustrated in FIG. 14 and employed by the vibration isolator type coupling fan, complex forces including forces in an axial direction, forces in a rotary direction, forces in a radial direction and the like act on the extending members 401. As a result, torsional forces act on the extending members 401. Hence, when the extending members 401 have a narrow width, there has been a fear for breakages of the extending members 401 which result from metal fatigue.